1. Field of the Invention
The present invention relates in general to control drives and in particular to a new and useful polarized electromagnetic drive, preferably for actuating a turning servo valve.
2. Description of the Prior Art
The term "polarized electromagnetic drive" as used in the present application refers to an electromagnetic transducer for converting electric input signals supplied in the form of electric currents, into proportional mechanical output quantities, such as torque, force, angle of rotation, or displacement. Polarized electromagnetic drives, known as control or torque motors, may be used also for controlling servo valves. Usually, they operate through only a small angle of rotation or over a small distance, for example, within an angular range of up to about two degrees, thus within the range of proportionality between the output and input variables. With the angle of rotation exceeding about two degrees, the output quantity varies, relative to the input quantity and conditional upon the system, following an exponential function, so that in this range, there is no longer a proportionality between the input and output variables, wherefore this range, which extends over more than a half of the geometrically possible region, usually cannot be utilized. An extension of the angular range beyond about two degrees, while simultaneously preserving the proportionality between the input and output quantities and transmitting the same force or torque, may be obtained in electromagnetic drives of the prior art only by increasing the total volume.